This invention relates to a lubrication system for a turbomachine and in particular to a system having a primary lubricating oil pump directly driven by the rotor of the turbomachine.
Generally, in turbomachine lubrication systems, the main or primary and standby or auxiliary oil pumps are independently driven through such means as electric motors. However, in some turbomachines, it has been found desirable to have the primary lubricating oil pump directly driven by the rotor of the turbomachine. At relatively low turbomachine operating speeds, the primary oil pump, when directly connected to the turbomachine rotor, cannot maintain a sufficient oil flow to meet the lubrication needs of the turbomachine. For example such minimum turbomachine operating speeds may occur during startup or shutdown of the turbomachine. As would be expected, the standby oil pump is energized during such periods of time since the auxiliary oil pump is independently driven to provide the necessary lubricating oil flow.
At other times, it may become necessary to energize the standby oil pump if the lubricating oil temperature should exceed a predetermined level to increase the relatively low temperature flow of lubricating oil from the oil sump to the portions of the turbomachine requiring same.
In either case, it has been found necessarry to maintain a flow of lubricating oil through the primary oil pump as the primary oil pump will continue to operate so long as the rotor of the turbomachine is rotating. In the absence of a minimum flow of oil through the primary oil pump the oil pump will overheat resulting in damage thereto. In essence, the pump will overheat due to the generation of frictional heat which cannot be dissipated in the absence of a continuous flow of lubricating oil.